Cambridge Audio 540A user manual Introduction, About this amplifier

INTRODUCTION

Thank you for purchasing this Cambridge Audio azur series amplifier. It is the result of our most extensive ever research and development program in over three decades of producing high quality audio products. We hope that you will appreciate the results and enjoy many years of listening pleasure.

About this amplifier

The design of any purist audio amplifier is mainly centred on two main areas, the Power Supply and the driver stage's ability to drive the output stage effectively. We at Cambridge Audio have researched the best possible ways to achieve the highest performance in these areas, at a sensible price. The Azur 540A/640A topology uses the same tried and tested output devices that Cambridge Audio have used in previous award winning amplifier models, but many hours of research have gone into the study and development of the preceding stages. This driver circuitry is essentially a matched differential input pair, loaded by a current mirror and driven from a transient compensated current source driving a high beta cascoded voltage gain stage. The thermally compensated output stage is setup to inherently give optimum Class AB conditions (for greatly reduced cross over distortion caused by dynamic heating of the output dies). In addition the topology includes a further improvement to the driver stage consisting of a pure class-A follower to isolate the voltage amplifier transistors from the difficult loading of the output transistors. This increased current drive to the output stage combined with a novel transient feed forward circuit doubles the slew rate to 40V/uS.

Due to critically refined circuit board layouts, careful component placement and short signal paths the stability of these amplifiers is extremely high which allows the compensation components to be

reduced in size. This has the effect of reducing distortion, increasing dynamics and allowing the bandwidth to be opened up to a massive 80kHz, ideal for the new 'better than CD' high bandwidth sources such as DVD-Audio and Super Audio CD.

The performance of any amplifier is limited by the dynamic abilities of its power supply, and for this reason Cambridge Azur amplifiers incorporate many features, including a low flux toroidal transformer, paralleling of the reservoir capacitors and careful use of bypass capacitors, to allow the instantaneous clean delivery of charge whenever it is needed. This ensures an open and natural sound being reproduced and ensures a positive response to any dynamics or sudden transients in the signal being reproduced.

Particular attention has also been paid to the quality of the passive components which have been carefully chosen for their sonic benefits. The Azur 640A in addition uses high grade Polypropylene signal bypass capacitors to improve signal flow and dynamics.

The Cambridge Audio Azur 540A and 640A amplifiers also incorporate tone controls, which may be switched out of circuit in 'direct' mode for the shortest and therefore purest signal path. Other features include 24k gold plated phono sockets, dual tape loops, pre amp output, a headphone socket and a secondary set of high level loudspeaker terminals.

An important feature which has been included as standard on both the 540A and 640A is the new innovative Cambridge Audio designed CAP5 protection system. This consists of a microprocessor which constantly monitors the amplifier providing comprehensive protection against a variety of possible faults. This has been achieved without adding any active circuitry into the signal path to degrade the sound or the dynamic abilities of the amplifier.

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